1. Field of the Invention
This invention relates to a method and system to form deletion windows on any coated glass substrate using an enamel paint to temporarily cover such areas during the reflective coating application, and then remove it by burning such enamel leaving exposed the desired opening areas on the glass (deletion windows).
2. Description of the Related Art
On the current automotive glass market there has been an increasing need for glasses that prevent the solar radiation from penetrating into the automobile cabin causing undesired heat and for causing additional fuel consumption to operate the air conditioning system for longer periods of time trying to cool it down. A well known solution known to automotive glass manufacturers are the reflective coated glasses that use a multilayer metallic coat applied using a coater as described in U.S. Pat. No. 4,166,018 to Airco, to reflect a big portion of the Infra Red spectrum of the solar light (700 to 2500 nanometers wavelength). The reflective property is given by one or several layers of silver nano particles applied in between other specialized metallic coats, as described in U.S. Pat. Nos. 6,445,503 by Guardian, 7,807,248 by Cardinal or 7,037,588 by Glaverbel.
Typical glass coating compositions for a triple silver layer system including: glass; TiO2 (layer1); ZnO (layer 2); Ag (layer 3); NiCr (layer 4); SnO2 (layer 5); ZnO (layer 6); Ag (layer 7); NiCr (layer 8); SnO2 (layer 9); ZnO (layer 10); Ag (layer 11); NiCr (layer 12); SnO2 (layer 13); and Si3N4 (layer 14).
The problem with this solution is that all those metallic coats also act as a barrier for the Electro Magnetic Fields commonly used in the transmission of signals (Radio, GPS, Garage door openers, TV, Toll Road Cards, etc.). Another problem is the corrosion caused when the coat is in direct contact with the atmospheric elements (humidity, acid rain, cleaning agents, etc). A simple solution for this problem has been the addition of areas where the metallic coat is removed, either strategically located or at a minimum all around the edge of the glass; these areas are commonly named “deletion windows” and act as access ports for all those electromagnetic signals and, in case of edge deletion, they seal the reflective coat from the effect of the atmospheric elements.
Currently there are different methods and systems to generate opening areas on coated glass consisting mainly of methods to attack the coating by: abrasion, laser, plasma or chemicals. The actual coat removal methods and systems are associated with high operating cost mainly due to the high defective rate coming from the coat damage due to handling and the need for specialized production processes to avoid any contact with the coat that is extremely fragile.
For example, U.S. Pat. No. 5,449,312 of Peter Lisec, describes a device for cutting a glass sheet with the help of a cutting tool, which can be rotated around an axis perpendicular to a supporting surface for the glass sheet to be machined, and for removing a coating, applied on the glass sheet, with the help of a grinding tool, which removes the coating from the glass sheet in strips lying on both sides of the scratch lines, running parallel to the grinding tool, with a beam, which is guided movably over the supporting surface on its edges, and with a cutting tool, as well as a grinding tool, which are guided movably on the beam along the same path. Those mechanisms allow the grinding wheel to be moved through the areas where the coat is to be removed.
However, this method requires special attention to the grinding wheel condition and the cleanliness of the working area since a worn out wheel can cause permanent damage to the glass or an uneven coat removal.
The method and system is limited in precision and cannot handle tight radius or narrow-small size areas very well, due to the fact that the grinding wheel contact area, the applied pressure and the form are changing with use.
An alternative method which in fact is a derivation of the grinding wheel method is the one developed by Saint Gobain (US patent application US2007/0090092 A1) where the grinding wheel is replaced by plasma heads that depending on their size and form a system will move such heads around the glass surface turning the plasma on and off according to the deletion windows design.
Advantages of this innovative system are cleanliness and the precision of the form removed area. This application suggests high operational cost. Also under this scenario the coated glass needs to be handled with extra care to avoid handling damage. However, the production equipment capable to handle coated glass with minimal damage is highly expensive and also requires costly maintenance routines.
Other alternative to remove the glass coating is shown in the U.S. Pat. No. 5,986,234 of Matthews, et al, which describes a compact laser system that removes surface coatings (such as paint, dirt, etc.) at a removal rate as high as 1000 ft2/hr or greater without damaging the surface. A high repetition rate laser with multiple amplification passes propagating through at least one optical amplifier is used, along with a delivery system consisting of a telescoping and articulating tube which also contains an evacuation system for simultaneously sweeping up the debris produced in the process. The amplified beam can be converted to an output beam by passively switching the polarization of at least one amplified beam. The system also has a personal safety system which protects against accidental exposures.
However, one problem with this method is that the time taken by the laser to remove the material is too long, making it unsuitable for large areas like the ones expected on automotive products. Maintenance and operational cost of the laser generator is also very expensive.
In other industries, such as fiber optic production and installation, they have adopted a method where special chemicals that dissolve the external coat are applied on the fiber to expose the fiber only on the specific area that is required.
For example, a method for removing a coating from a portion of optical fiber is described in U.S. Pat. No. 6,582,527 of Marazzi, et al. This method consists of immersing the coated fiber in a special acid. The acid will dissolve only the coating material, while exposing the fiber without causing any damage.
The method described in U.S. Pat. No. 6,582,527, even though it is interesting is extremely risky to be used with large pieces like automotive windshields. During the process the portion of the coat that needs to remain on the glass must be covered to be protected from the acid to avoid damages in case of spills. This makes this process extremely complicated and not suitable for our purposes.
Other problems associated with processing coated glass is the fragility of the coat itself. The coat is an exposed composition of ultra thin layers of metallic components like oxides that can be easily damaged by corrosion and or abrasion. This coat increases its chemical and mechanical resistance once it is heated above 620° C. (after bending), where it can be handled in a manner similar but not the same as the standard methods due to the properties of the coat.
Based on the above the purpose of this invention is to accomplish the processing of automotive (reflective laminated sidelites or windshields) or architectural glass (energy efficient windows) that can contain, as part of their design, deletion windows of a controlled form and size and or edge deletion areas.
In accordance with the above, the present invention considers the application of the coating to a precut and premasked deletion areas on the glass using instead a special enamel cut to form and then remove the coat starting from a glass bracket with the coat already on its surface.
With the proposed method, the glass with no coat will be handled on regular production lines with no risk of damage to the coat because it is not as yet on the glass, thus eliminating the need of large investments on specialized production lines. To generate the deletion windows, the proposal is to use an organic enamel, which can be applied with the current serigraphic painting machines, widely used in the automotive glass fabrication process, then to dry this paint using a regular IR oven. This will provide enough mechanical resistance to the enamel for the handling, packing, shipping and washing prior to the glass coater. Another characteristic of this proposed enamel is that it will not release any component into the coater atmosphere avoiding any kind of contamination.
It is important to note that under this proposed method and system, there is no limitation with respect to the glass forms and deletion windows designs. All that is needed is a new printing screen with the desired window form and size and to paint this pattern over the glass to be coated.
Another important benefit is that the glass can be stored under regular conditions, not like the coated glass that demands special temperature and humidity (≦50%) control to avoid the metallic coat becoming oxidized.